Hours after the Jakarta blasts, investigators focus on a Malaysian regarded as a key ideological leader of the terrorist group, which had not staged a major attack in four years.

The restaurant in the Ritz-Carlton, where many foreign businesspeople congregate, was nearly hollowed out by the blast there, the buffet bar sagging as, incongruously, several decorative bottles sat untouched. Authorities said the explosives contained nails.

At the Hilton, not far away, guards inspected arriving vehicles and guests were required to pass through metal detectors. But a Western guest who arrived Friday night, just hours after the explosions, was not asked to open a laptop bag similar to the one carried by the bombers. A guard asked if there was a computer inside, then let the man pass.

Hundreds of Jemaah Islamiyah members are spread across more than 10,000 islands that make up Indonesia, the Philippines, Malaysia and Singapore.

The group had not launched a significant attack since October 2005. U.S. counter-terrorism officials monitoring its members have documented fewer instances of plotting, fundraising and recruiting, several officials said in interviews Friday.

The group was also believed to have been significantly degraded by the arrest of hundreds of its members, from foot soldiers to leaders.

But the network has also proved extremely resilient, aided in part by U.S. and allied focus on the growing threat posed by Al Qaeda in Pakistan, said Dailey, a retired lieutenant general and former top Pentagon special operations official.

A handful of Jemaah Islamiyah commanders -- particularly Top -- have managed to elude a dragnet by hiding among supporters. Top has used disguises, aliases and other measures to avoid detection, Dailey said.

Authorities consider Top one of the most charismatic of Islamist militants operating anywhere in the world, particularly because of his ability to persuade others to launch suicide bombings, including the attacks on Bali nightclubs in 2002 that killed 202 people.

"The ability to get people to blow themselves up requires a certain talent, and he has it," said Zachary Abuza, an expert on Jemaah Islamiyah who advises various governments on its tactics and structure.

Top is also considered one of Jemaah Islamiyah's most successful recruiters and strategists, and was given the nickname the Moneyman because he is thought to be an important fundraiser for the group, with direct ties to Al Qaeda in Pakistan, said Abuza, a professor at Simmons College in Boston who travels frequently to Southeast Asia.